Layer Formations in Electron Beam Sintering

Among direct metal processing manufacturing technologies (Rapid Manufacturing), Electron Beam Sintering (EBS) exhibits a high application potential. Especially, the fast beam deflection provided by electromagnetic lenses allows the realization of considerable building speeds and minor residual stresses. Therefore, this paper aims to examine and utilize the given potential for additive layer manufacturing. In this context, the deployed scanning strategy is a very important aspect. By means of an increasing computer power, innovative and flexible patterns for the solidification of the powder can be implemented. Thus, different patterns are being examined and evaluated. Finally, occurring effects in the exposed zone are introduced.Mechanical Engineerin

T-matrix computations for particles with high-order finite symmetries

The use of group theoretical methods can substantially reduce numerical ill-conditioning problems in T-matrix computations. There are specific problems related to obtaining the irreducible characters of high-order symmetry groups and to the construction of a transformation from the basis of vector spherical wave functions to the irreducible basis of high-order symmetry groups. These problems are addressed, and numerical solutions are discussed and tested. An important application of the method is non-convex particles perturbed with high-order polynomials. Such morphologies can serve as models for particles with small-scale surface roughness, such as mineral aerosols, atmospheric ice particles with rimed surfaces, and various types of cosmic dust particles. The method is tested for high-order 3D-Chebyshev particles, and the performance of the method is gauged by comparing the results to computations based on iteratively solving a Lippmann-Schwinger T-matrix equation. The latter method trades ill-conditioning problems for potential slow-convergence problems, and it is rather specific, as it is tailored to particles with small-scale surface roughness. The group theoretical method is general and not plagued by slow-convergence problems. The comparison of results shows that both methods achieve a comparable numerical stability. This suggests that for particles with high-order symmetries the group-theoretical approach is able to overcome the illconditioning problems. Remaining numerical limitations are likely to be associated with loss-of-precision problems in the numerical evaluation of the surface integrals

Prosuming, or when customers turn collaborators: coordination and motivation of customer contribution

This article investigates the phenomenon of increasing integration of customers and users into the organizational creation of value, focusing primarily on the dissolving boundaries between production and consumption. Concepts such as "prosuming", the "working customer", "produsing" and "interactive value creation" have been used to describe this phenomenon. Within the framework of a research project at the Goethe-University Frankfurt/Main, this debate was investigated theoretically as well as empirically in three case studies. The research question is as follows: Why do customers participate in "new types of prosuming" or "interactive value creation" and how are these processes coordinated by the firms? The results show a considerable range of motives and forms of coordination: The customers’ primary motives to voluntarily assume tasks and activities were both intrinsic and extrinsic in nature. The organizational models identified range from strategies of rationalization to prosuming as a basic business model to the collaborative and interactive value creation between the company and the web-community

Optical properties of marine aerosol: modelling the transition from dry, irregularly shaped crystals to brine-coated, dissolving salt particles

An aerosol-optics model for water-coated marine aerosols is introduced that accounts for irregularities in the geometry of dry salt particles, and that mimics the processes of water-adsorption, dissolution of salt, and rearrangement of the liquid mantle following dissolution. The model can be tuned to adjust how rapidly the dry salt particles become spherical as water is being added to them. Size-shape distributions of the model are generated and employed to compute the ensemble-averaged extinction and backscattering cross sections, the lidar ratio, and the linear backscatter depolarisation ratio (LDR). A power law distribution that is frequently used in chemical transport models yields lidar ratios and LDR values that are consistent with field and satellite observations. But the results are found to be quite sensitive to the assumed size distribution. A generic lognormal size distribution tends to produce higher extinction cross sections, backscattering cross sections, and somewhat higher lidar ratios than the power-law distribution, while the depolarisation ratios are of comparable magnitude. We further gauged the model\u27s performance by comparing it with homogeneous superellipsoids. For a salt mass fraction of 0.97, the cross sections and the lidar ratio of cubic superellipsoids (i.e., those with unit aspect ratios) agree best with the reference model over all effective radii at a superellipsoid roundness parameter of 0.6. The LDR is more challenging to reproduce. For a salt mass fraction of 0.97, cubic homogeneous superellipsoids mostly give lower LDR values than the reference model. However, by increasing one aspect ratio, the superellipsoids can be tuned to yield higher LDR values. For a salt mass fraction of 0.91, the reference model yields LDR values below 0.1. Homogeneous superellipsoids that match the cross sections and lidar ratio of the reference model tend to give LDR values exceeding the reference results, at least for super-micron particles

Checking semantics in UML models

Modeling is one of the most crucial activities during all the phases in any software development life cycle. Typically, system development is a very complex task, and working with models helps to handle this complexity in an organized way, allowing us to reason about the properties that entities possess. In software engineering, notation, techniques and methodology for object-oriented model building has been lately the focus of active research work. In the case of object-oriented software development, models are composed by a number of communicating and well delimited elements. Although such models are sometimes harder to develop, they are easier to understand, and simpler to maintain and modify.Thus, reusability of elements among models is enhanced. In order to maximize these properties, we need tools that support the process of object- oriented development by serving as repository of previously asserted knowledge, checking the integrity of the model and maintaining the different views that form each model. Consequently, it is expected this automatic control will reduce the manual, error-prone work of maintaining model consistency across all life cycle phases. UML, Unified Modeling Language is a graphical language for visualizing, specifying, constructing and documenting the elements of a software intensive system. UML provides notation for expressing the model, in the form of graphic and text elements. Attached to these elements, there is a semantic interpretation that attempts to capture the meaning of the model, and it is represented by the constraint mechanism. Constraints are one of the three extensibility mechanisms that UML introduces, although currently the language for expressing them is not standard (natural language or OCL can be used for this purpose). Supporting tools for object oriented development in UML should not only provide a graphic editor for the notation, but also help to ensure the coherence of its semantics aspects. This research line attempts to formalize the consistency check process in UML models.Eje: Ingeniería de SoftwareRed de Universidades con Carreras en Informática (RedUNCI

Models for integrated and differential scattering optical properties of encapsulated light absorbing carbon aggregates

Optical properties of light absorbing carbon (LAC) aggregates encapsulated in a shell of sulfate are computed for realistic model geometries based on field measurements. Computations are performed for wavelengths from the UV-C to the mid-IR. Both climate- and remote sensing-relevant optical properties are considered. The results are compared to commonly used simplified model geometries, none of which gives a realistic representation of the distribution of the LAC mass within the host material and, as a consequence, fail to predict the optical properties accurately. A new core-gray shell model is introduced, which accurately reproduces the size- and wavelength dependence of the integrated and differential optical properties

Disk and circumsolar radiances in the presence of ice clouds

The impact of ice clouds on solar disk and circumsolar radiances is investigated using a Monte Carlo radiative transfer model. The monochromatic direct and diffuse radiances are simulated at angles of 0 to 8° from the center of the sun. Input data for the model are derived from measurements conducted during the 2010 Small Particles in Cirrus (SPARTICUS) campaign together with state-of-the-art databases of optical properties of ice crystals and aerosols. For selected cases, the simulated radiances are compared with ground-based radiance measurements obtained by the Sun and Aureole Measurements (SAM) instrument. First, the sensitivity of the radiances to the ice cloud properties and aerosol optical thickness is addressed. The angular dependence of the disk and circumsolar radiances is found to be most sensitive to assumptions about ice crystal roughness (or, more generally, non-ideal features of ice crystals) and size distribution, with ice crystal habit playing a somewhat smaller role. Second, in comparisons with SAM data, the ice cloud optical thickness is adjusted for each case so that the simulated radiances agree closely (i.e., within 3 %) with the measured disk radiances. Circumsolar radiances at angles larger than ≈ 3° are systematically underestimated when assuming smooth ice crystals, whereas the agreement with the measurements is better when rough ice crystals are assumed. Our results suggest that it may well be possible to infer the particle roughness directly from ground-based SAM measurements. In addition, the results show the necessity of correcting the ground-based measurements of direct radiation for the presence of diffuse radiation in the instrument's field of view, in particular in the presence of ice clouds.Peer reviewe

Heat-shock mediated overexpression of HNF1β mutations has differential effects on gene expression in the Xenopus pronephric kidney.

The transcription factor HNF1B, encoded by the TCF2 gene, plays an important role in the organogenesis of vertebrates. In humans, heterozygous mutations of HNF1B are associated with several diseases, such as pancreatic β-cell dysfunction leading to maturity-onset diabetes of the young (MODY5), defective kidney development, disturbed liver function, pancreas atrophy, and malformations of the genital tract. The African claw frog Xenopus laevis is an excellent model to study the processes involved in embryogenesis and organogenesis, as it can be manipulated easily with a series of methods. In the present study, we overexpressed HNF1β mutants in the developing Xenopus embryo to assess their roles during organogenesis, particularly in the developing pronephric kidney. Towards this goal, we developed a heat-shock inducible binary Cre/loxP system with activator and effector strains. Heat-shock activation of the mutant HNF1B variants P328L329del and A263insGG resulted in malformations of various organs and the affected larvae developed large edemas. Defects in the pronephros were primarily confined to malformed proximal tubules. Furthermore, the expression of the proximal tubule marker genes tmem27 and slc3a1, both involved in amino acid transport, was affected. Both P328L329del and A263insGG downregulated expression of slc3a1. In addition, P328L329del reduced tmem27 expression while A263insGG overexpression decreased expression of the chloride channel clcnk and the transcription factor pax2. Overexpression of two mutant HNF1B derivatives resulted in distinct phenotypes reflected by either a reduction or an enlargement of pronephros size. The expression of selected pronephric marker genes was differentially affected upon overexpression of HNF1B mutations. Based on our findings, we postulate that HNF1B mutations influence gene regulation upon overexpression in specific and distinct manners. Furthermore, our study demonstrates that the newly established Cre/loxP system for Xenopus embryos is an attractive alternative to examine the gene regulatory potential of transcription factors in developing pronephric kidney as exemplified here for HNF1B

A T matrix method based upon scalar basis functions

A surface integral formulation is developed for the T matrix of a homogenous and isotropic particle of arbitrary shape, which employs scalar basis functions represented by the translation matrix elements of the vector spherical wave functions. The formulation begins with the volume integral equation for scattering by the particle, which is transformed so that the vector and dyadic components in the equation are replaced with associated dipole and multipole level scalar harmonic wave functions. The approach leads to a volume integral formulation for the T matrix, which can be extended, by the use of Green's identities, to the surface integral formulation. The result is shown to be equivalent to the traditional surface integral formulas based on the VSWF basis